- eventually will clean up IntelliSense -- removing classes users don't
need when editing a view
- will _not_ cleanup IntelliSense 'til VS stops using a private copy of
Microsoft.AspNet.Mvc.Razor.Host.dll or we update that copy
- all tests and MVC sample views still work fine
- issue #969
- use Microsoft.AspNet.Mvc.Rendering namespace throughout assembly
Also
- move `IdAttributeDotReplacement` from `TagBuilder` to `HtmlHelper`
- remove commented-out code in `HtmlHelper`
- use `var` and `[NotNull]` more
- `String` -> `string`
- correct Resources references; add missing resources
This is as simple as modifying the base class to return task and await the ExecuteAsync method. Also added a piece to the sample project to verify functionality.